1. Field of the Invention
The present invention relates to a valve moving apparatus of an internal combustion engine, particularly to a valve spring set load changing device in a valve moving apparatus for changing set load of a valve spring of an engine valve in accordance with operational condition of the internal combustion engine.
2. Description of the Related Art
Hitherto, set load of a valve spring of an engine valve, namely an intake valve or an exhaust valve, has been set based on inertia force of a valve moving system at the highest rotational speed of the engine so that jumping and bounce of the engine valve does not occur even by inertia force of the valve moving system at the highest rotational speed. Since the inertia force increases in proportion to a square of rotational speed of the engine, the set load of the valve spring is also set at a value proportional to a square of the rotational speed. Therefore, at low and middle rotational speed region of the engine, the set load of the valve spring is unnecessarily large, so that rate of frictional output loss to engine output is increased.
Accordingly, various arts for changing set load of the valve spring in accordance with rotational speed of an internal combustion engine have been proposed. For example, Japanese Laid-Open Patent Publication Hei 10-299435 discloses a valve spring load changing apparatus for a moving valve of an internal combustion engine. In this apparatus, a spring seat of the valve spring for forcing the moving valve (intake valve or exhaust valve) in direction to open includes an upper seat supporting an end of the valve spring and a lower seat. A lower surface of the upper seat and an upper surface of the lower seat are formed with respective tapered surfaces and pressure receiving surfaces, and the upper and lower seats are houses in a seat case disposed on a recessed spring bearing seat on a cylinder head in a state that the tapered surfaces are contacted with each other so as to rotate relatively. The tapered surfaces, the pressure receiving surfaces and the seat case form an oil pressure chamber of a hydraulic actuator.
When the engine is in a low rotational speed region and pressure in the oil pressure chamber is low, the upper seat occupies a lower limit position in a state that the pressure receiving surfaces of the upper and lower seats are contacted with each other. When the engine is in a high rotational speed region and pressure in the oil pressure chamber is high, the upper and lower seats rotate relatively in a state that the tapered surfaces are contacted with each other while the upper seat rises from the lower limit position, then the upper seat is held at a balanced stop position corresponding to the oil pressure. Thus, spring force of the valve spring increases in proportion to increase of the rotational speed.
According to the above-mentioned related art, since the hydraulic actuator including the spring seats is formed within the seat case and the cylinder head must be provided with a circumferential wall of a specific height for forming the recessed spring bearing seat housing the seat case, a relatively wide and high zone around the spring seat is occupied by the seat case and the spring bearing seat. Moreover, each of the intake valves and the exhaust valves require the hydraulic actuator and the spring seat. Therefore, a part of the cylinder head around the spring seat becomes large to make the entire cylinder head large and heavy, and degree of freedom of arrangement of the intake valves and the exhaust valves is restricted.
The present invention has been accomplished in view of the foregoing. According to the valve spring set load changing device of the present invention, it can be restrained that the cylinder head is made large and heavy, and arrangement of engine valves is restricted little. Further, stable and certain change of the set load and cost reduction of the internal combustion engine can be intended. And a set load can be maintained stably.
The present invention provides a valve spring set load changing device in a valve moving apparatus of an internal combustion engine having an engine valve for opening and closing a port of a combustion chamber connected with an intake passage or an exhaust passage, a valve spring for forcing the engine valve in a closing direction, a spring seat for supporting an end of the valve spring and a cam for opening the engine valve against the valve spring, wherein the spring seat includes a base seat and a support seat supporting the end of the valve spring and movable relatively to the base seat, the base seat and the support seat are provided with a direction changing mechanism for changing relative movement between the base seat and the support seat into movement of the support member in direction of expansion and contraction of the valve spring, an actuator for generating a drive force in accordance with an operational condition of the internal combustion engine and a manipulating mechanism connected with the actuator are provided outside of the spring seat, and at least one of the support seat and the base seat constitutes a driven seat driven by the drive force transmitted through the manipulating mechanism to cause the relative movement of a predetermined amount for- changing set load of the valve spring.
According to this invention, when the drive force generated by the actuator is transmitted to the driven seat through the manipulating mechanism, a relative movement is caused between the support seat and the base seat, and the relative movement is changed into a movement of the support member in direction of expansion and contraction of the valve spring by the direction changing mechanism to change set load of the valve spring. The driven seat is driven through the actuator and the manipulating mechanism disposed outside of the spring seat and it is required only that the manipulating mechanism engaging with the driven seat is disposed in the neighborhood of the spring seat. Therefore, arrangement of the engine valve is restricted little.
Since a manipulating mechanism separated from the cylinder head can be disposed in a portion around the spring seat, a part of the cylinder head around the spring seat is not enlarged, so that it can be restrained that the entire cylinder head becomes large and heavy. Since the manipulating mechanism and the driven seat can be engaged with each other in any position around the spring seat, degree of freedom of arrangement of the driven seat and the manipulating mechanism is large, and arrangement of the engine valve is restricted little by the set load changing device.
The manipulating mechanism may have a rod connected to the actuator, and an engaging section of the rod and an engaging section of the driven seat may be engaged with each other to connect the driven seat with the manipulating mechanism.
Since the driven seat is driven through the rod connected to the actuator, the actuator can be disposed at a place distant from the spring seat, for example, at an end portion of the cylinder head. As the result, degree of freedom of arrangement of the actuator becomes large and arrangement of the engine valve is almost not restricted by the set load changing device.
The internal combustion engine may have a cylinder head provided with an insertion hole for inserting a ignition plug or a fuel injection valve facing the combustion chamber, and the rod may be disposed between the engine valve and the insertion hole.
The rod is disposed utilizing a relatively narrow space between the engine valve and the ignition plug or the fuel ignition valve. As the result, the manipulating mechanism can be disposed within the cylinder head compactly and enlargement of the cylinder head can be restrained.
The internal combustion engine may have the engine valves with the respective driven seats, and the driven seats may be connected with a single manipulating mechanism.
Since the driven seats for the respective engine valves is driven by the single manipulating mechanism, number of parts is reduced, assembling is easy, and enlargement and increase in weight of the cylinder head can be restrained.
The support seat may support a plurality of the valve springs.
Since some valve springs are supported by a common support seat, number of parts is reduced, number of actuators and manipulating mechanisms is also reduced, assembling is easy, and restriction of arrangement of other members by the set load changing device is few.
Preferably, the drive force of the actuator is set so that the driven seat is driven to cause the relative movement of the predetermined amount only when the engine valve is closed, the manipulating mechanism has a elastic deformation member storing the drive force generated by the actuator, and the drive force is transmitted to the driven seat through the elastic deformation member.
If drive force of the actuator acts on the driven seat through the manipulating mechanism when the engine valve is closed, the valve spring is elongated and spring force of the valve spring is the minimum, the relative movement of the predetermined amount is caused between the support seat and the base seat, and the support seat is moved in direction of expansion and contraction of the valve spring by the direction changing mechanism so that set load of the valve spring is changed. If the actuator generates the drive force in case the engine valve is opened when the valve spring is more compressed and spring force of the valve spring is larger compared with the case the engine valve is closed, the drive force of the actuator acts on the driven seat through the elastic deformation member. However, since spring force of the valve spring is larger than that in case the engine valve is closed, the driven seat can not be moved so as to cause the relative movement of the predetermined amount. Therefore, the elastic deformation member is deformed to store the drive force. When the cam rotates further and the engine valve is closed to reduce spring force of the valve spring to the minimum, the driven seat is driven by the drive force stored in the elastic deformation member, the relative movement of the predetermined amount is caused between the support seat and the base seat and set load of the valve spring is changed. In case that plural driven seats for respective engine valves are driven by a common manipulating mechanism, set loads of the valve springs are changed in order when respective engine valves are closed.
Thus, if the drive force of the actuator is previously set at a specific value capable of driving the driven seat when the engine valve is closed, the set load can be changed stably and certainly at a specific time, that is, when the engine valve is closed. Since there is no need to adjust timing of generating the drive force, a control system of the actuator becomes simple and cost of the engine is reduced. This is the same in case that plural driven seats are driven by a common manipulating mechanism.
Preferably, the support seat has a first position where the set load of the valve spring is set at a first set value and a second position where the set load of the valve spring is set at a second set value larger than the first set value by movement of the support seat in direction to contract the valve spring, and at the second position, the base seat and the support seat comes into contact with each other through contact surfaces on a plane right-angled to a line of action of spring force of the valve spring.
Because at the second position where the set load is larger the base seat and the support seat comes into contact with each other through contact surfaces on a plane perpendicular to a line of action of spring force of the valve spring, even if a large spring force acts on the support seat and the base seat when the engine valve is opened, no component force to slip the base seat and the support seat relatively is not generated, and fluctuation of the set load can be prevented.
Therefore, even when the support seat is positioned at the second position and the large spring force acts, relative movement between the base seat and the support seat is prevented, and the set load set in accordance with an operational condition of the engine can be maintained stably.